Avian influenza (AI)--the bird flu--is a virus that infects wild birds (such as ducks, gulls, and shorebirds) and domestic poultry (such as chickens, turkeys, ducks, and geese). There is flu for birds just as there is for humans and, as with people, some forms of the flu in birds are worse than others.

AI classification: viruses are classified by a combination of two groups of proteins: the hemagglutinin or H proteins, of which there are 16 (H1-H16), and neuraminidase or N proteins, of which there are 9 (N1-N9). There are 144 possible combinations or subtypes based upon this classification scheme.

Pathogenicity: the ability of the virus to produce disease in poultry. AI strains also are divided into two groups based upon this ability of the virus to produce disease: low pathogenic (LP) and highly pathogenic (HP).

LPAI, or "low path" avian influenza, naturally occurs in wild birds and can spread to domestic birds. In most cases it causes no signs of infection or only minor symptoms in birds. These strains of the virus pose little threat to human health. LPAI H5 and H7 strains have the potential to mutate into HPAI and are therefore closely monitored.

HPAI, or "high path" avian influenza, is often fatal in chickens and turkeys. HPAI spreads more rapidly than LPAI and has a higher death rate in birds. HPAI H5N1 is the type rapidly spreading in some parts of the world.

Biosecurity: Precautions taken to minimize the risk of introducing an infectious disease into an animal population.

Eradicate: to destroy or get rid of the avian influenza virus completely, so that it can never recur or return.

Virus Isolation: this is the gold standard test used to diagnose AI virus infections. The virus is isolated in embryos inside chicken eggs. A series of tests follow to specifically identify H and N subtypes of the AI virus.

Genetic Sequence: the process of determining the individual elements that make up a specific gene. This could be equated to finding the "blueprint" of the gene.

Chicken Pathogenicity Test: this test involves the inoculation of 4 to 8 week old disease-free chickens and observation for signs of AI for 10 days. According to the USDA and the World Organization for Animal Health, highly pathogenic AI is defined as any AI virus that is lethal for 6 or more of 8 chickens (75% mortality).

Flyway Zone: a major route of travel for migratory birds. USDA is working with the Department of the Interior to sample birds for AI in Alaska, the Pacific flyaway; the Pacific islands; and the Central, Mississippi, and Atlantic flyways.

Environmental Sampling: waterfowl release AI viruses through the intestinal tract and the virus can be detected in both feces and water in which the birds swim. Environmental sampling entails testing the feces and water for AI viruses. Analysis of both water and fecal material from waterfowl habitat can provide evidence of avian influenza circulating in wild bird populations.

National Poultry Improvement Plan (NPIP): a voluntary cooperative federal, state and industry program designed to prevent the spread of poultry diseases in commercial poultry operations.

Sample Collection: testing for the presence of AI requires that samples be taken from live birds, dead birds or the environment birds inhabit. Samples are routinely collected from wild birds, domestic flocks, live bird markets and quarantined birds.

Tracheal Swab: samples from the airway in birds through which air moves from the throat to the lungs.

Cloacal Swab: samples from the common opening in birds through which intestinal, urinary, and reproductive tracts empty.

Properly Prepared Poultry: cooking poultry to 165° Fahrenheit kills the AI virus as it does other bacteria and viruses. Cooking eggs until they are firm throughout kills the AI virus. AI is not transmissible by eating properly prepared poultry.

National Veterinary Services Laboratories (NVSL): at the Federal level, USDA's NVSL in Ames, Iowa serves as the national veterinary diagnostic and confirmatory laboratory. NVSL coordinates activities, participates in methods validation, and provides training, proficiency testing, assistance, materials, and prototypes for diagnostic tests. NVSL is the only AI reference laboratory in the United States recognized by the World Organization for Animal Health, known as the OIE. Although there is a network of laboratories across the nation approved to conduct AI screening tests, confirmatory testing in the United States is conducted only at NVSL.

National Animal Health Laboratory Network (NAHLN): a cooperative effort between two USDA agencies-the Cooperative State Research, Education, and Extension Service and the Animal and Plant Health Inspection Service-and the American Association of Veterinary Laboratory Diagnosticians. It is a multifaceted network comprised of sets of laboratories that focus on different animal diseases using common testing methods and software platforms to process diagnostic requests and share information. These labs run preliminary tests for AI and determine if an AI virus is present and whether it is an H5 or H7 subtype. Because of the potential for H5 or H7 subtypes to mutate into highly pathogenic strains, those samples are forwarded to USDA's National Veterinary Services Laboratories (NVSL) for confirmatory testing.